No, she's absolutely right. The majority of Disneyland guests on any given day outside of July/August are annual pass holders. The majority of annual pass holders have SoCal local passes. They will be blocked by then, and the summer tourism rush hasn't quite kicked in by mid-June. It's one of the nicest times to be at the park - everything is open and rides running at maximum capacity, but not as many guests as in July or August. But thanks to the park running a full summer schedule and capacity on rides, lines move fast.
Finding Nemo is an anomaly - it's in incredibly slow loading and low capacity attraction, whose lines can be long just because it takes 20 minutes to rotate on sub through a cycle.
It won't be empty by any means, but the lack of locals helps. The wildcard is what kind of, if any, SoCal ticket deal is offered for non-pass holders, who might want to take advantage of seeing Cars Land early.
